In an RFID system, an RFID reader may be required to distinguish between and communicate with a large number of different RFID tags within a given communication range. Where each of the different RFID tags is identified by a unique identification number, it is imperative that the RFID reader be able to quickly and accurately read the identification number associated with each tag. However, when the communication channel between the RFID reader and tags becomes corrupted by noise, the ability of the RFID reader to quickly and accurately identify the RFID tags may be impaired.
Previous RFID readers typically use some variation of an algorithm for reading a population of RFID tags. The algorithm seeks to sequentially read the tags ordered from strongest to weakest return signals. After each RFID tag is read, it is shut down. No information is carried over from tag read to tag read. Although this technique is simple to implement in the RFID reader, it is not very robust in the presence of noise.
One major application of RFID systems is electronic inventory. In modem business, maintaining an accurate inventory of merchandise is crucial. In the past, taking inventory was an entirely manual process, and therefore slow and expensive. In an RFID electronic inventory system, an RFID tag is attached to each item to be inventoried. Each RFID tag is assigned a unique tag identification number.
In a typical application, multiple tagged items are stacked on a pallet. Readers are located at various points in the distribution chain to read and inventory the tagged items. For example, one or more readers may be located at a dock door. As the pallet moves through the dock door, a reader interrogates the population of tags on the pallet. Tags on items in the interior of the stack tend to have weaker signals than exterior tags due to their signals having to pass through more items of the pallet than exterior tags. As a result, the signals of interior tags may be difficult to read. In addition, many of the RFID inventory applications operate in noisy RF environments.
Consequently, a need therefore exists for an alternative technique that permits an RFID reader to efficiently read a population of RFID tags in a manner that is robust to noise and that optimally utilizes past information gained by the RFID reader, other RFID readers, or other systems compiling information for RFID readers, during or before the reading process.
A further need exists for a method of communicating between an RFID reader and a population of RFID tags that maximizes the read rate and accuracy of weakly responding RFID tags.